The invention relates to a belaying device for a rope, comprising:                a support plate equipped with a fixed stud,        a cam mounted with limited rotation on the support plate around a first spindle-pin and having a peripheral sector around which the rope is wound, said cam being movable between a securing position corresponding to the rope being blocked by a jamming effect against the stud and a separated position enabling the rope to run freely in the gap between the cam and the stud.        